Only anions can gain electrons in ionic bonds. This includes oxygen, however, when an oxygen atom gains two electrons, it becomes negatively charged. This is the charge that people identify on the Periodic Table. In which one oxygen atom needs two more electrons to have a full valence shell.
As a result, the anion has a notation of
The reason why it is not
Hope this helps :)
As we all know that an atom or molecule without charge is a neutral particle(used for atom or molecules)to maintain the electrical balance.
So when ever we add or remove electrons we are making the particles charged.
Adding electrons will increase the negative charge over a particle and not a positive.
Cause Increasing electrons increases negative charge as the electrons carry negative charges and not a positive one. :)
So the protons in the atom/molecules just neutralizes
the same amount of electrons and the extra electrons will impart their character.
So adding electrons increases negative charge and decreasing electron increases positive charge :)